Recently, personal communications technology as an extension of development of a cordless telephone technology has been progressed. And attention is focused on a wireless PBX (Private Branch eXchange) system which was developed based on this personal communication technology.
With respect to this wireless PBX system, as a result of further search and development of the mobility along with the development of wireless technology of telephone sets, it cam to be apparent that the wireless PBX system can be used not only in a service area under the control of a single wireless PBX system but also with respect to a movable area between PBXs by means of automatic registration of a current location of a given end system without a need of compelling a user or subscriber to make a meaningless change of registration (or activation of transmission of an incoming signal or the like).
On the other hand, there is currently an increasing need of a data communication through the Internet. There are two types of data communication methods; the first one is a method by way of a telephone line (line switch) and the second one is a method for performing a communication from a terminal device accommodated in a LAN. The method of using a LAN is mostly employed in the in-enterprise communication.
In this in-enterprise communication, it sometimes becomes necessary to use a system which is capable of performing a packet data communication across various physical networks as represented by a LAN such as Ethernet, etc. In order to perform a routing of packet data between end terminal devices across the various physical networks, it is required that each terminal device can uniquely be identified. To this end, each terminal device is assigned for use with an address (packet address) on a virtual network as represented by an IP (Internet Protocol) address, etc.
Hereinbefore, the Internet, which is based on the wireless PBX system where a data communication is performed chiefly by way of line switching and the LAN, has been described. The former is coming to be well accepted as a main communication means in many offices by applying mobility thereto, while the latter is becoming a main communication means for data communication.
Incidentally, a new data communication system is currently being searched and developed. In this new system, a wireless PBX system and a LAN are coupled and a data communication terminal device is connected to a personal station located in the wireless PBX system so that a data communication can be performed between this data communication terminal device and a data communication terminal device on the LAN side.
In the above case, in order to transmit packet data to the data communication terminal device under the control of the wireless PBX system from the LAN side, it is necessary for the LAN side to identify an IP address of that data communication terminal device because the data communication terminal device under the control of the wireless PBX system is one of the network terminal devices having a series of different physical addresses.
In order to deliver the above packet data to the particular data communication terminal device through the wireless PBX system, it is necessary that the wireless PBX system side identifies a physical address of the particular data communication terminal device, i.e., physical address of a personal station to which the specific data communication terminal device is connected, while referring to the IP address and that the wireless PBX system forms a physical link between the personal station and the LAN.
In order to form such a physical link, the IP address must primarily be determined from the IP address. To this end, there are required such complicated procedures that a connective relationship between each data communication terminal device and each personal station is fixed, or a means for obtaining a corresponding relationship between each data communication terminal device and each personal station is provided within the system, and so forth.